Danling Tang

Upwelling in the Taiwan Strait during the summer monsoon detected by satellite and shipboard measurements

The Taiwan Strait is located at the confluence of the East China Sea and the South China Sea in the west Pacific Ocean. Several upwelling zones in the Taiwan Strait are noted for their high fisheries production; these upwelling zones have been studied in the past decade, but we have no overall picture on the size and temporal changes of these upwelling zones due to only limited in situ observation over short periods of time. The present paper investigates upwelling in the Taiwan Strait with satellite remote sensing data of NOAA-derived Sea Surface Temperature (SST) and SeaWiFS-derived Chlorophyll-a (Chl-a) and shipboard measurements during summer 1998. Results reveal five upwelling zones: (1) coastal upwelling near Pingtan Island (PTU), (2) coastal upwelling between Meizhou and Xiaman (MXU), (3) big coastal upwelling near Dongshan Island (DSU), sometimes extending to offshore, (4) small occasional upwelling near the Penghu Island (PHU) and (5) an intensive upwelling in the Taiwan Bank (TBU). TBU was extensively studied over summer 1998. Results showed that the TBU looks like a banana in shape in the southern edge of the Taiwan Bank; it intensifies in its southeastern edge. The size of TBU was about 2500–3000 km 2 , with a mean value of 2796 km 2 . The temperature difference between the upwelling and non-upwelling areas was about 2.5–3.5 jC for early August with a mean value of 2.3 jC on July to October. Series of images indicated a short-term variation of TBU and showed that high Chl-a concentrations (up to 0.8–2 mg m 3 ) zones coincided with low SST (25–26 jC) zones in terms of location, time, and shape. These upwelling zones change with size and intensity center from time to time. Field measurements of water temperature, salinity, and Chl-a in 1998 are consistent with satellite measurements. D 2002 Elsevier Science Inc. All rights reserved.

Seasonal and spatial distribution of chlorophyll-a concentrations and water conditions in the Gulf of Tonkin, South China Sea

The Gulf of Tonkin is a semi-closed gulf northwest of the South China Sea, experiencing reversal seasonal monsoon. Previous studies of water conditions have been conducted in the western waters of the gulf, but very few studies of the Chlorophyll-a (Chl-a) distribution have been carried out for the entire gulf. The present study investigates seasonal and spatial distributions of Chl-a and water conditions in the Gulf of Tonkin by analyzing Sea-viewing Wide Field-of-View Scanner (SeaWiFS) derived Chlorophyll-a (Chl-a), in situ measurements, sea surface temperatures (SST), and other oceanographic data obtained in 1999 and 2000. The results show seasonality of Chl-a and SST variations in the Gulf of Tonkin, and reveal phytoplankton blooming events in the center part of the gulf during the northeast monsoon season. In summer, Chl-a concentrations were relatively low (<0.3 mg m 3 ) and distributed uniformly throughout most of the area, with a belt of higher Chl-a concentrations along the coast, particularly the coast of Qiongzhou Peninsula; in winter, Chl-a concentration increased (0.5 mg m 3 ) in the entire gulf, and phytoplankton blooms offshore-ward from the northeast coast to the center of the gulf, while Chl-a concentrations reached high levels (0.8–1 mg m 3 ) in the center of the blooms. One peak of Chl-a concentrations was observed during the northeast monsoon season in the year. SST were high (27–29 jC) and distributed uniformly in summer, but lower with a large gradient from northeast (17 jC) to southwest (25 jC) in winter, while strong northeast winds (8–10 m/s) were parallel to the east coast of the gulf. Comparison of Chl-a values shows that SeaWiFS derived Chl-a concentrations match well with in situ measurements in most parts of the gulf in May 1999, but SeaWiFS derived Chl-a are higher than in situ data in river mouth waters. The seasonal variation of Chl-a concentrations and SST distribution were associated with the seasonally reversing monsoon; the winter phytoplankton blooms were related to vertical mixing and upwelling nutrients drawn by the northeast wind. D 2003 Elsevier Science Inc. All rights reserved.

Remote sensing oceanography of a harmful algal bloom off the coast of southeastern Vietnam

[ 1] Harmful algal blooms (HABs) in the southeastern Vietnamese coastal waters have caused large economic losses in aquacultured and wild fisheries in recent years; however, there have been few oceanographic studies on these HAB events. The present study reports an extensive HAB off southeastern Vietnamese waters during late June to July 2002 with in situ observations and analyzes the oceanographic conditions using satellite remote sensing data. The HAB had high chlorophyll a ( Chl a) concentrations ( up to 4.5 mg m-3) occurring -200 km off the coast and -200 km northeast of the Mekong River mouth for a period of -6 weeks. The bloom was dominated by the harmful algae haptophyte Phaeocystis cf. globosa and caused a very significant mortality of aquacultured fish and other marine life. In the same period, sea surface temperature (SST) imagery showed a cold water plume extending from the coast to the open sea, and QuikScat data showed strong southwesterly winds blowing parallel to the coastline. This study indicated that the HAB was induced and supported by offshore upwelling that brings nutrients from the deep ocean to the surface and from coastal water to offshore water and that the upwelling was driven by strong wind through Ekman transport when winds were parallel to the coastline. This study demonstrated the possibility of utilizing a combination of satellite data of Chl a, SST, and wind velocity together with coastal bathymetric information and in situ observations to give a better understanding of the biological oceanography of HABs.

Occurrences of harmful algal blooms (HABs) associated with ocean environments in the South China Sea

Harmful algal blooms (HABs) occur frequently in the South China Sea (SCS), causing enormous economic losses in aquaculture. We analyzed historical HAB records during the period from 1980 to 2003 in SCS. We found that HABs-affected areas have expanded and the frequency of HABs varied during this period. The seasonal and annual variations, as well as causative algal species of HABs are different among the four regions. Areas with frequent HABs include the Pearl River Estuary (China), the Manila Bay (the Philippines), the Masinloc Bay (the Philippines), and the western coast of Sabah (Malaysia). HABs occurred frequently during March–May in the northern region of SCS, May–July in the eastern region, July in the western region, and year-round in the southern region. Among the species that cause HABs, Noctiluca scintillans dominated in the northern region, and Pyrodinium bahamense in the southern and eastern regions. Causative species also varied in different years for the entire SCS. Both P. bahamense and N. scintillans were the dominant species during 1980–2003. Some species not previously recorded formed blooms during 1991–2003, including Phaeocystis globosa, Scrippsiella trochoidea, Heterosigma akashiwo, and Mesodinium rubrum. Variations in HABs are related to various regional conditions, such as a reversed monsoon wind in the entire SCS, river discharges in the northern area, upwelling in Vietnam coastal waters during southwest winds and near Malaysia coastal waters during northeast winds, and eutrophication from coastal aquaculture in the Pearl River estuary, Manila Bay, and Masinloc Bay.

AVHRR satellite remote sensing and shipboard measurements of the thermal plume from the Daya Bay, nuclear power station, China

The 1800 MW Daya Bay Nuclear Power Station (DNPS), Chinas first nuclear power station, is located on the coast of the South China Sea. DNPS discharges 29 10 x 10(5) m(3) year(-1) of warm water from its cooling system into Daya Bay, which could have ecological consequences. This study examines satellite sea surface temperature data and shipboard water column measurements from Daya Bay. Field observations of water temperature, salinity, and chlorophyll a data were conducted four times per year at 12 sampling stations in Daya Bay during January 1997 to January 1999. Sea surface temperatures were derived from the Advanced Very High Resolution Radiometer (AVHRR) onboard National Oceanic and Atmospheric Administration (NOAA) polar orbiting satellites during November 1997 to February 1999. A total of 2905 images with 1.1 x 1.1 km resolution were examined; among those images, 342 have sufficient quality for quantitative analysis. The results show a seasonal pattern of thermal plumes in Daya Bay. During the winter months (December to March), the thermal plume is localized to an area within a few km of the power plant, and the temperature difference between the plume and non-plume areas is about 1.5 degreesC. During the summer and fall months (May to November), there is a larger thermal plume extending 8-10 kin south along the coast from DNPS, and the temperature change is about 1.0 degreesC. Monthly variation of SST in the thermal plume is analyzed. AVHRR SST is higher in daytime than in nighttime in the bay during the whole year. The strong seasonal difference in the thermal plume is related to vertical mixing of the water column in winter and to stratification in summer. Further investigations are needed to determine any other ecological effects of the Daya Bay thermal plume

Phytoplankton blooms near the Pearl River Estuary induced by Typhoon Nuri

The authors investigate two phytoplankton blooms near or off the Pearl River Estuary (PRE) triggered by Category 2 Typhoon Nuri with moderate wind intensity in the South China Sea using both remotely sensed and in situ data sets. An offshore triangular phytoplankton bloom (chlorophyll a (Chl a) > 0.5 mg m(-3)) was observed near Dongsha Archipelago along Nuris track, prolongating southeastward to 18 degrees N 1 week after the typhoons passage; a stronger nearshore phytoplankton increase (Chl a > 1.5 mg m(-3)) with high total suspended sediment appeared southwest of the PRE from the coast toward the South China Sea. After the typhoons passage, sea surface cooling (similar to 3 degrees C), strong wind (> 20 m s(-1)), and heavy rainfall (> 100 mm d(-1)) were also observed in the region, especially offshore. In addition, the freshwater discharge from the PRE during the typhoon passage increased fivefold in comparison with the August climatology in the nearshore bloom region. The nearshore bloom was probably due to the increased discharge from the PRE and favorable current, as well as mixing, upwelling, and near-inertial resonance driven by strong typhoon wind. The offshore bloom may be triggered by upwelling and entrainment induced by strong typhoon wind and the topography of islands and islets. The present study suggests that one typhoon may nourish phytoplankton biomass by inducing transport of nutrient-rich water from both the Pearl River Estuary to offshore and the sublayer to surface.

Effect of 1998 El Niño on the distribution of phytoplankton in the South China Sea

[ 1] The present study analyzed interannual variation of phytoplankton/ Chlorophyll-a (Chl-a) distribution in the South China Sea (SCS) for the period from 1997 to 2005 using SeaWiFS-derived Chl-a data and other oceanographic data. The results show high spatial variation of Chl-a concentrations in the SCS and revealed an anomalous event in 1998. High Chl-a concentrations in the southwestern SCS in the summer season ( June to August) may be related with strong Ekman Pumping and strong wind stress, whereas a jet-shape high Chl-a region offshore in western SCS was associated with coastal upwelling driven by offshore Ekman transport and Vietnamese offshore current. Chl-a concentrations in 1998 summer in the SCS were the lowest among the 7 years and were particularly low in the western SCS. At the same season, the jet-shape Chl-a region offshore of southeast Vietnam almost disappeared, and southwesterly monsoon winds and offshore current were relatively weaker in 1998. This anomalous event of low phytoplankton biomass in the SCS coincided with an El Nino year in 1998.

Multi-sensor studies of the Sumatra earthquake and tsunami of 26 December 2004

Multi sensor satellites are now capable of monitoring the globe during day and night and provide information about the land, ocean and atmosphere. Soon after the Sumatra tsunami and earthquake of 26 December 2004, multi‐sensors data have been analysed to study the changes in ocean, land, meteorological and atmospheric parameters. A pronounced changes in the ocean, atmospheric and meteorological parameters are observed while comparing data prior and after the Sumatra main event of 26 December 2004. These changes strongly suggest a strong coupling between land, ocean and atmosphere associated with the Sumatra event.

Seasonal phytoplankton blooms associated with monsoonal influences and coastal environments in the sea areas either side of the Indochina Peninsula

The Gulf of Thailand (GoT) is a semienclosed sea on the west and southwest side of the Indochina Peninsula and connects with the near-coastal waters of the South China Sea (SCS) on the east and northeast side of the Malay Peninsula. The objective of the present study is to understand dynamic features of the phytoplankton biology in the GoT and the nearby SCS, on both sides of the Indochina Peninsula, using remote-sensing measurements of chlorophyll-a (Ch1 a), sea surface temperature (SST), and surface vector winds obtained during the period from September 1997 to March 2003. Results show that seasonal variations of the phytoplankton blooms are primarily controlled by the monsoonal winds and related coastal environments. The GoT and the near-coastal SCS have a peak in the averaged monthly Ch1 a in December and January, which is associated with the winter northeaster monsoon. The near-coastal SCS have another big peak in the averaged monthly Ch1 a in summer (July to September), which is associated with the summer southwest monsoon. The offshore bloom in the GoT occurs in its southern part and enhances the December-January peak of averaged monthly Ch1 a. By contrast, the offshore bloom in the nearby SCS is observed northeast of the Peninsula, and represents the primary source of the July-September peak Ch1 a. Here the coastal upwelling associated with the offshore Ekman transport caused by the coastal surface winds parallel to the Vietnam east coast gives physical conditions favorable to the development of offshore phytoplankton blooms. The Mekong River discharge waters flow in different directions, depending on the monsoon winds, and contributes to seasonal blooms on both sides of the Peninsula.

Eddy-feature phytoplankton bloom induced by a tropical cyclone in the South China Sea

This is the first report on an eddy-feature phytoplankton bloom induced by a tropical cyclone (the spiral structure of the bloom was coincident with that of a cold eddy) in the South China Sea (SCS). Applying satellite data, this report can furnish fresh evidence of the relationship between the bloom and the cold eddy. Tropical cyclone Linfa passed over the northern SCS from 16 to 21 June 2009. While it looped over for 2 days (from 17 to 19 June), a cold eddy, which lasted for 11 days in the looping area, was observed on 18 June. Subsequently, an eddy-feature phytoplankton bloom (central location: 18° N, 117.5° E) was detected on 22 June and it remained for 17 days. The character of both the cold eddy and the bloom was rotating counterclockwise, with two arms. High Ekman pumping velocity (>4.5 × 10−4 m s−1) was estimated during the passage of Linfa (from 17 to 19 June). The monthly climatology of the mixed layer depth was about 20 m in June, and the maximum Ekman layer depth was about 346 m after Linfa. The analysis indicated that Linfa may have induced the cold eddy, where it looped around. With upwelling and entrainment, the eddy potentially provided nutrients to the bloom in the surface water. The results suggested that the sea surface current changes that Linfa induced had caused the bloom in an eddy feature. Tropical cyclones appear frequently in the SCS, which may affect the activities of mesoscale eddies in this area.